1. Field
The present invention relates to a method for manufacturing a semiconductor device suitable for a ferroelectric memory.
2. Description of the Related Art
In recent years, a ferroelectric memory (FeRAM) that stores information in a ferroelectric capacitor by utilizing the polarization inversion of a ferroelectric has been developed. The ferroelectric memory is a nonvolatile memory wherein information does not disappear even when the power supply is shut off, and can realize high integration, high-speed driving, high durability, and low power consumption. As the materials for a ferroelectric film that composes the ferroelectric capacitor, ferroelectric oxides that have a perovskite crystal structure having a large residual polarization quantity, such as PZT (Pb(Zr, Ti)O3) and SBT (SrBi2Ta2O9) are mainly used. The residual polarization quantity of PZT is about 10 to 30 μC/cm2.
In the same manner as in other semiconductor devices, ferroelectric memories are tested even after manufacturing.
Conventionally, an accelerated test has been conducted as the above-described test.
According to such a test, not only chips that do not correctly operate after manufacturing, but also chips that do not correctly operate thereafter in a short time can be eliminated.
However, the present inventors found that acceptable ferroelectric capacitors were damaged due to the above-described test, and their lives were shortened. The present inventors also found that when the relationship between the voltages applied to the ferroelectric film and polarization quantities was plotted on the graph, a highly symmetrical hysteresis loop was obtained; however, when the above-described test was conducted, the hysteresis loop was transited and symmetry was lost. Such a phenomenon may be called “imprint”. If the hysteresis loop is transited even once, it does not return to the original position.
As described above, in the present test, a problem wherein effect to the characteristics of the ferroelectric capacitors cannot be suppressed has been caused.